Method of separating uranium values, plutonium values and fission products by chlorination



1959 H. s. BROWN ET AL 2,87

METHOD OF SEPARATING URANIUM VALUES, PLUTONIUM VALUES PRODUCTS BY CHLORINATION Filed'Aug. 24, 1945 AND FISSION we S ates listen w 1 2,815,011 r1101) FSEPARATING URAN PLUTONIUM VALUES AND FISSIQN PR Doors BY'CHLORINATION' IUNi 1VA Harrison St Brown and Glenn F T. is eabbrg Chica'go,- 11].,

- assignors -:to the United statespf-America as represented by the United States Atomic-EnergyComrnission Application August 24, 1943, sesame 499,762

' is Claims. (01. 23-14;

substantially fall J I other sulqstances esul i g fron lflhe neutronbombardment of thefltiranium Further"objects-and"advantages will be apparent from the following:"description and drawing". f y t 'In the drawingQthe figure'is ai'diagr ammatic view in section .of an apparatus for carrying, out one process embodying the invention. 'In thetolloWihg' description,"the isotope of element 9.3 having a mass'x'of 239 is ref'e'rredftoas' 9 3 and the isotope of element 94jhaving a mass of 239 is' referred to as 94 j Ele'rnentQ-s may alsobe spoken of as plutonium, symbol Pu. Referen'cesto' anyof the elemerits will include the element either'in its free state or" as a compound. Neutronirra'diated-uranium may be prepared by'reacting uranium with' neutrons from aiiyconventionalneutronsource,but preferably the neutrons used are obtained Neutroni irradiated uranium contains "93 produced through betadecay a'sa result'of the'react'io'n of'neutrons U 94 1'formed from the beta decay of 93 and; also a' l'argenumber of radioactive fission products from a chain reactionof neuand more. particularly relates to the resulting rorn' the neutron bombardment of uranium.

'ltfa'lso contains'rninor amounts of the natural radioactive decay productssuch'as UX and UX The 93 plus"9 4 'is genera lly present in very' smallamounts ,and,,'since 111693 has a half'life of"onl'y' ,23 days and decaysg'to 94 the 94 generally-will be present 'in'larger proportion than the 93 By storing the neutron irradiatedfuranium for-several days, the 93 may be converted "almost entirely 'to 943. The'f fiss'ion products are present in very smallanioun'ts, butfb ecause of their high :products be removed. 7 p

The fission products consistof'a' large number 'ofele- Inents which may be classified into two groups, alight group with atomic numbersfrom' 35-'44;-and aheavy group with atomic "nun1bers' from 51-58. 'The'fiss'ion fprod'ucts withwhich'"'we are particularly concerned are .those having a, half life of more than {three days since theyremain'in the reactioirmass'in substantial quantities at least onemonth"afterreaction. These"produ"cts are chiefly 81- :Y (57 ,day ,half life),

the group "of atomic numbers 1' from 3 5-44; and Te T6 I fXe Cs (many years half-life), Ba (12 *'days' half life)-," Lal P', andfCe 0f 2O day "and 200- ,day

inclusive;

radioactivity, is highly desirablethat'these nium chloride is lower 'of plutonium with the ninth, it is desirable 'ismos't easily treated. The uranium may be treated most satisfactori1y'whenin the form of the 2,875,021 .Batented Feb. .24,,195'

nium chlorides. The latter product is volatilized at controlledtemperatures and removed'from plutonium and other substances in vapor form as. a separate fraction. Plutonium is separated from the remaining substances by being volntilized as a reaction product at higher temperatures and removed in vapor form as a second separate'fraction.

"The separation of the uranium from plutonium probably results either from the fact that the temperature of.,formation of uranium'pentachloride or higher urathan the temperature of reaction chlorine or'fromthe fact that the temperature of volatilization' of the reacted uranium is lower than that of the reactedplutonium. Irrespective of the explanation, it has been found that uranium and plutoniumwill be volatilized and separated from each other an'dffrom other substances present when treated in accordance'with the invention.

"Whileithe uranium to be treated is preferably neutron irradiated uranium, it is contemplated that any uranium containing plutonium with or without other substances present may be v separated treated as described herein. As only relatively small amounts of plutonium, fission products, andother substances are contained in the urato have the uranium in a form which from such plutonium when metal or, preferably, asone'of 'the'ur'anium oxides. If the uranium" is I originally in the form of a compound other than'an oxide,

it is "desirable to convert such compound" to the oxide before separating the substances present. Where the uranium 'is 'in"thefform of a metal, it may be advantageous toconve'rtsuchfmetal touranium oxide although the metal may' be' treated directly. Of the severalura- 'nium"'oxides,'1. nranium tritaoctoxide, U 0 is most conveniently used;

In using uraniumoxide, it is desirable to have present a substancewhich will unite with the the latter will be removed from the uranium, as where of carbon dioxide orca'rbon monoxide or both. Various oxygen-removing substances may be usedeither in liquid form, such as carbon tetrachloride, chloroform, antimony chloride, and the like, or insolidform, such as charcoal'orgraphite. It iscontemplated that an oxygen- I I removing substance may'be used in gaseous form.

"stance, the uraniumoxidel is contained in a receptacle 2 which will expose a largeamountj of surface of the uranium oxide. The;ree,eptacle is, placed in a reaction chamber '3, which like' an. other parts fofrthe apparatus isformed oflma terial, such as ,glass o17 -the. like,.-.which will tnotrbe seriously corroded; or: otherwise deteriorated by the action of-chlorine or other substances; present. :If desired, the uranium oxide may be, placed 1 directly in the reaction chambefwithout being containedin receptacle 1.

rTh'e: :reaction; chamber "3, has 'an aperture 4 .so positioned that gases entering the chamberxthrough such" aperture 1 will-come into 'intimate' bontact with the =uraniutn oxide. half lives fromthegroupdiatomicnumbersffrom SE58 carbon tetrachloride 6. Gaseous chlorine is introduced into receptacle from chlorine tank 7 by means of pipe 8 which extends almost to the bottom of receptacle 5 thereby causing the chlorine to pass up through the carbon tetrachloride and through aperture 4. The carbon tetrachloride is kept warm by suitable heating means (not shown) so that it will v'ap'orizemore easily and be carried with the chlorine into the reaction chamber 3 and into intimate contact with the uranium oxide.

Where the oxygen-removing substance is in solid form, such as charcoal or graphite, the substance is intimately mixed with the uranium oxide in one to twice the theoretical proportionsnecessaryforthe carbon to unite with the oxygen of the oxide to form carbon dioxide. Thus, from 48 to 96 grams of carbon may be'used for every 842. grams of uranium tritaoctoxide, U 0 The chlorine is passed directly-from tank 7 through aperture 4 into the reaction chamber 3. v

In using the uranium metal without an oxygen-removing substance, the uranium is placed in reaction chamber 3 and the chlorine supplied, directly from tank 7.

An excess of chlorine over that necessary to complete- 7 1y react with the uranium and the substances contained therein is passed into reaction chamber 3. The pressure under which the chlorine is present in the reaction chamber influences the reaction. If greater pressure is used, the reaction proceeds faster and heat is evolved more rapidly. As the temperature of the uranium oxide during the reaction must be controlled, it is desirable that the chlorine pressurebe adjusted to the temperature of the uranium oxide during the reaction. Satisfactory results are obtained by using one atmosphere pressure of the chlorine in the reaction chamber and controlling the temperature of the uranium oxide during the reaction by heating means.

During the reaction of the uranium oxide with the chlorine and the oxygen-removing substance, reaction chamber 3 is maintained at a sufficiently high temperature by a suitable heating device, such as heating coil 9, to cause the reacted uranium to be volatilized, such temperature being sufficiently low to prevent any substantial volatilization of the plutonium and other substances present. It has been found that the uranium will be volatilized where the temperature is below 500 C. while the plutonium remains in a substantially non-volatile state. Preferably, the temperature of the uranium oxide during the reaction is' approximately 450 C. where the chlorine is under a pressure of one atmosphere in the reaction chamber.

As chlorine 1s passed over the uranium, the latter reactswith the chlorine to form one or more uranium chlorides higher than uranium tetrachloride, such as uranium pentachloride and possibly small amounts of uranium hexachloride. Either of these chlorides are suitable as their volatility is sufiiciently greater than that of plutonium or its reaction product to permit the uranium to be volatilized and removed while the plutonium is non-volatile. If desired, the details of the process may be varied to cause formation of a preponderance of a volatile uranium chloride, such as uranium hexaehloride, other than uranium pentachloride. In its broadest aspect, the inventionincludes reacting uranium and chlorine to form a uranium reaction product which will be su'fiiciently more volatile than 'plutonium or its chlorine reaction product or products 'to permit the uranium to be volatilized and removed while the plutonium is ina substantially non-volatile state. -Where higher uranium chloride is mentioned in the following, it is toinclude urauiumchlorides higher than uranium tetrachloride, such as uranium pentachloride or uranium hexachloride or mixtures of such chlorides.

- Where'uranium isin the form-of an. -oxide and'an o y en-r mov n s b e: s. p n a d i react n Pr duc s a e termed u h astca bpn d x e ca b uranium chloride passes out of the reaction chamber 3,

it carries with it substances which are desired to be separated from the uranium, such as plutonium, fission products, or other substances originally present in the uranium oxide. While many of such substances may not be considered volatile at the temperature of the reaction chamber, they, nevertheless, pass out of the chamber with the higher uranium chloride. In passing through trap chamber 11, at least some of the carried substances are deposited upon the glass wool while the higher uranium chloride, excess chlorine, carbon dioxide, the relatively more volatile fission products, and the like, passon through. The trap chamber is preferably maintained at a temperature of approximately 200 C. by suitable heating means, such as a heating coil 12.

After passing. out of the trap chamber through aperture 13, the higher uranium chloride is forced by valve I 14 tqpass through pipe 15 into condensing chamber -16 which is preferably maintained at room temperature. of the more volatile fission products is deposited upon the interior surfaces of condensing chamber 16 while the carbon dioxide, excess chlorine, and other waste gases pass out of the condensing chamber through aper- 'f ture 17 and are disposed of. The higher uranium chloride and any fission products may be removed from the interior surfaces of condensing chamber 16 by washing with Water, scraping, volatilizing, or the like.

The substances remaining in reaction chamber 3 include plutonium which is separated from thev other substances present by being volati-lized at a higher temperature. The flow of chlorine is maintained through the reaction chamber but the temperature of the substances present is raised to 700 C.-800 C. by heating coil 9. Plutonium is volatilized at this temperature in the presence of chlorine and passes out of the reaction chamber through aperture 10. The volatilized plutonium passes throughtrap chamber 11 and into aperture 13 where it is forced by valve 14 through pipe 18 into condensing chamber 19 which is maintained at room temperature. The volatilized plutonium is deposited upon the interior surfaces of condensing chamber 19, while the excess chlorine and other Waste gases pass out through aperture 20 and are disposed of. The deposited plutonium may be removed from condensing chamber 19 by washing with water, scraping, volatilizing, or the like.

The higher uranium chloride which has been collected as a separate fraction in condensing chamber 16 contains negligible amounts of plutonium and moderate amounts of radioac ive fission products. If desired, the uranium may be furt er purified.

Plutonium, which has been collected as a substantially separate fraction in condensing chamber 19, contains small amounts of fission products and substantially no uranium.

The substances remaining in reaction chamber 3 comprise substantial amounts of the radioactive fission products originally present in the uranium oxide. These may be removed from the reaction chamber and considered as a substantially separate fraction. Mmor amounts of The higher uranium chloride together with any I radioactive fission tially all of the uranium as a separate fraction. It is also contemplated that this step may be used in conjunction with other methods of separating plutonium from the fission products or other substances in the residue to obtain the plutonium and such other substances as substantially separate fractions. 1

In one embodiment of the invention, one gram of U containing minute amounts of plutonium and fission products is treated with gaseous chlorine under one atmosphere pressure, the chlorine having passed through approximately 5 'cc. of carbon tetrachloride 6. The uranium oxide 1 is treated with chlorine and carbon tetrachloride for approximately one-half hour during which time the temperature of reaction chamber 3 is maintained at 450 C. Volatile higher uranium chloride is formed which passes through trap chamber 11 and into condensing chamber 16. The condensed higher uranium chloride contains approximately 30 percent of products and approximately 7 percent of plutonium. Substantially all of the uranium is removed from the reaction chamber during the reaction.

After the higher uranium chloride is removed, the temperature of reaction chamber 3 is raised to approximately 700 C. and chlorine is passed over the remaining substances under pressure of one atmosphere for approximately one-half hour. At the end of this time, substantially all of the plutonium is volatilized and has passed out of the reaction chamber through trap chamber 11 and into condensing chamber 19. The condensed plutonium contains approximately 5 percent of radioactive fission products and substantially no uranium.

The residue is removed from reaction chamber 3 and contains a substantial amount of the radioactive fission products together with minute amounts of other substances.

The substances, such as plutonium, UX which are carried from reaction chamber 3 tilized uranium reaction and the like, by the volaproduct may usually be considered as non-volatile. While the reason for such behavior is not definitely kno such carrying may result from the fact that where extremely minute amounts of substances are treated the volatilization behavior, especially when considered with respect to the forces of attraction between the surfaces of the apparatus and the substances, is not the same as where larger amounts of the substances are treated. Consequently, in a relatively large scale process, it is possible that the problem of preventing substances from being carried out of the reaction chamber by the volatilized uranium product may not be present. In such a-case,.the trap chamber 11 may be dispensed with and the volatilized reaction product carried directly to condensing chambers 16 and 19.

The carrying phenomenon may be prevented or re duced by means other than the use of glass wool or other inert material having a large surface area. Various holdback materials may be incorporated with the uranium oxide 1 or the uranium metal in reaction chamber 3. As used in the specification and claims, the term holdback material refers to materials that are incorporated with the uramum compound prior to volatilization of the uranium chloride and that do not interfere with the volatilization and removal of the uranium, but do prevent or reduce the carrying over or removal of other substances present.

Holdback materials which have been used satisfactorily are lanthanum oxide, La O and thorium oxide, ThO

In one case, 1.4 mg. of lanthanum oxide were mixed with 30 mg. of uranium tritaoctoxide and treated with chlorine and carbon tetrachloride. The loss of UX one of the substances carried by the volatilized uranium, was one percent as compared with a 50 percent loss where the holdback material was not used. In another case, 2.2 mg. of thorium oxide were mixed with 30 mg. of uranium tritaoctoxide and the mixture treated as before. The loss of UX was 0.5 percent as compared again to the 50 percent loss Where no holdback material was used. The volatilization or removal of substances from the reaction chamber other than UX is likewise prevented or reduced by such holdback materials.

Where the uranium treated is neutron irradiated uranium, the particular amounts of fission products and plutonium which are present in the uranium will depend somewhat upon the amount of time which is allowed to lapse between the neutron bombardment of the uranium and the process of separation.

The above detailed description is given for purposes of illustration and the invention is to be limited only by the scope of the appended claims.

What is claimed is:

1. A method of separating uranium values from plutonium values comprising contacting said uranium with chlorine in the presence of a holdback material selected from the group consisting of lanthanum oxide and thorium oxide to form a uranium chloride higher than uranium tetrachloride, and thereafter heating the uranium chloride thus formed to a temperature at which said uranium chloride is volatilized off but below the volatilization temperature of plutonuim chloride.

2. A method of separating uranium values, plutonium values, and fission products comprising contacting a uranium oxide containing plutonium and fission products with chlorine in the presence of a holdback material selected from the group consisting of lanthanum oxide and thorium oxide to form a uranium chloride higher than uranium tetrachloride, thereafter heating the uranium chloride thus formed to a temperature below 500 C. but suficiently high to volatilize off said uranium chloride from said plutonium values and at least a part of said fission products, contacting said plutonuim with chlorine to form a plutonium chloride, and thereafter heating the plutonium chloride thus formed to a temperature of about 700 C. to volatilize off said plutonium chloride from at least a part of said fission products.

3. A method of separating uranium values, plutonium values, and fission products comprising contacting said uranium with chlorine in the presence of a holdback material selected from the group consisting of lanthanum oxide and thorium oxide to form a uranium chloride higher than uranium tetrachloride, thereafter heating the uranium chloride thus formed to a temperature below 500 C. but sufliciently high to volatilize 011? said uranium chloride from said plutonium values and at least apart of said fission products, contacting said plutonium with chlorine to form a plutonium chloride, and thereafter heating the plutonuim chloride thus formed to a temperature of about 700 C. to volatilize off said plutonium chloride from at least a part of said fission products.

References Cited in the file of this patent UNITED STATES PATENTS DAdrian Nov. 7, 1922 OTHER REFERENCES 

1. A METHOD OF SEPARATING URANIUM VALUES FROM PLUTONIUM VALUES COMPRISING CONTACTING SAID URANIUM WITH CHLORINE IN THE PRESENCE OF A HOLDBACK MATERIAL SELECTED FROM THE GROUP CONSISTING OF LANTHANUM OXIDE AND THORIUM OXIDE TO FORM A URANIUM CHLORIDE HIGHER THAN URANIUM TETRACHLORIDE, AND THEREAFTER HEATING THE URANIUM CHLORIDE THUS FORMED TO A TEMPERATURE AT WHICH SAID URANIUM CHLORIDE IS VOLATILIZED OFF BUT BELOW THE VOLATILIZATION TEMPERATURE OF PLUTONUIM CHLORIDE. 